"coder1: adds code in the registration controller . ( 10 mins ) done."
And once your code accumulates enough of these 10-minute hack jobs, it becomes incomprehensible and unmaintainable, and every little change will break something. At that point, progress grinds to a halt. You'll then need someone like coder2, who has a talent for system architecture, to refactor them back to a sane state again. (I've been both coder1 and coder2, under different circumstances.)
And once your code accumulates enough of these 10-minute hack jobs, it becomes incomprehensible and unmaintainable, and every little change will break something. At that point, progress grinds to a halt. You'll then need someone like coder2, who has a talent for system architecture, to refactor them back to a sane state again. (I've been both coder1 and coder2, under different circumstances.)